It's not about yelling loud enough. There's an inherent wave in all things. It's science, but like I said, I didn't pay attention to whatever the hell we were talking about in Astronomy class that day. Though it's not a sonic boom or a loud enough yell to break anything, if you sync up with said inherent wave, there is a reaction. It's where the story about an opera singer breaking the crystal wine glasses comes from.

Harmonic frequencies could shatter glass. Opera singers can and have done this, it's been proven on Mythbusters even. A bell? Maybe. Stopping swords and killing birds with harmonic frequency is just plain idiotic and not supported by any science at all. Also, even if one could get the right frequency, they would also have to yell loud enough for the harmonics to have enough amplitude to cause damage.

"Those who can make you believe absurdities, can make you commit atrocities." – Voltaire.